Hey Whyte Ice,
When I write a song I figure out the vocal line by singing over the chord progression. Then I figure out on my guitar or keyboard what notes I'm singing if I need to write the vocal line out on paper.
My guess is that less then half of the singers in popular music today know what note they are singing at any given time. And I'll guess that close to 100% of classical singers can tell you what note they are singing at any given time.
If you don't know how to figure out what your singing you can learn some music theory by picking up a book or taking some lessons or a class.
Good luck,
scodu.